Aperiodic transmission method and appartus for sounding reference signal in wireless communication system

ABSTRACT

A method for transmitting, by a user equipment (UE), an aperiodic sounding reference signal (SRS) in a wireless communication system. The method includes receiving, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an SRS request for triggering transmission of an aperiodic SRS, detecting the SRS request, if a carrier indicator field (CIF) is configured, transmitting the aperiodic SRS on a uplink (UL) component carrier (CC), among a plurality of UL CCs, corresponding to the CIF, and if a CIF is not configured, transmitting the aperiodic SRS on a UL CC, among the plurality of UL CCs, in which a physical uplink shared channel (PUSCH) is scheduled by the DCI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of copending U.S. application Ser.No. 13/509,486, filed on May 11, 2012, which is the National Phase ofPCT/KR2011/001546, filed on Mar. 7, 2011, which claims priority under 35U.S.C. 119(a) to Korean Application No. 10-2011-0019404, filed in theRepublic of Korea on Mar. 4, 2011 and under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/310,712 filed on Mar. 5, 2010. Thecontents of all of these applications are hereby incorporated byreference as fully set forth herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for aperiodic sounding referencesignal in a wireless communication system.

2. Discussion of the Related Art

The next-generation multimedia wireless communication systems which arerecently being actively researched are required to process and transmitvarious pieces of information, such as video and wireless data as wellas the initial voice-centered services. The 4^(th) generation wirelesscommunication systems which are now being developed subsequently to the3^(rd) generation wireless communication systems are aiming atsupporting high-speed data service of downlink 1 Gbps (Gigabits persecond) and uplink 500 Mbps (Megabits per second). The object of thewireless communication system is to establish reliable communicationsbetween a number of users irrespective of their positions and mobility.However, a wireless channel has abnormal characteristics, such as pathloss, noise, a fading phenomenon due to multi-path, Inter-SymbolInterference (ISI), and the Doppler Effect resulting from the mobilityof a user equipment. A variety of techniques are being developed inorder to overcome the abnormal characteristics of the wireless channeland to increase the reliability of wireless communication.

Technology for supporting reliable and high-speed data service includesOrthogonal Frequency Division Multiplexing (OFDM), Multiple InputMultiple Output (MIMO), and so on. An OFDM system is being consideredafter the 3^(rd) generation system which is able to attenuate the ISIeffect with low complexity. The OFDM system converts symbols, receivedin series, into N (N is a natural number) parallel symbols and transmitsthem on respective separated N subcarriers. The subcarriers maintainorthogonality in the frequency domain. It is expected that the marketfor mobile communication will shift from the existing Code DivisionMultiple Access (CDMA) system to an OFDM-based system. MIMO technologycan be used to improve the efficiency of data transmission and receptionusing multiple transmission antennas and multiple reception antennas.MIMO technology includes spatial multiplexing, transmit diversity,beam-forming and the like. An MIMO channel matrix according to thenumber of reception antennas and the number of transmission antennas canbe decomposed into a number of independent channels. Each of theindependent channels is called a layer or stream. The number of layersis called a rank.

In wireless communication systems, it is necessary to estimate an uplinkchannel or a downlink channel for the purpose of the transmission andreception of data, the acquisition of system synchronization, and thefeedback of channel information. In wireless communication systemenvironments, fading is generated because of multi-path time latency. Aprocess of restoring a transmit signal by compensating for thedistortion of the signal resulting from a sudden change in theenvironment due to such fading is referred to as channel estimation. Itis also necessary to measure the state of a channel for a cell to whicha user equipment belongs or other cells. To estimate a channel ormeasure the state of a channel, a Reference Signal (RS) which is knownto both a transmitter and a receiver can be used.

A subcarrier used to transmit the reference signal is referred to as areference signal subcarrier, and a subcarrier used to transmit data isreferred to as a data subcarrier. In an OFDM system, a method ofassigning the reference signal includes a method of assigning thereference signal to all the subcarriers and a method of assigning thereference signal between data subcarriers. The method of assigning thereference signal to all the subcarriers is performed using a signalincluding only the reference signal, such as a preamble signal, in orderto obtain the throughput of channel estimation. If this method is used,the performance of channel estimation can be improved as compared withthe method of assigning the reference signal between data subcarriersbecause the density of reference signals is in general high. However,since the amount of transmitted data is small in the method of assigningthe reference signal to all the subcarriers, the method of assigning thereference signal between data subcarriers is used in order to increasethe amount of transmitted data. If the method of assigning the referencesignal between data subcarriers is used, the performance of channelestimation can be deteriorated because the density of reference signalsis low. Accordingly, the reference signals should be properly arrangedin order to minimize such deterioration.

A receiver can estimate a channel by separating information about areference signal from a received signal because it knows the informationabout a reference signal and can accurately estimate data, transmittedby a transmit stage, by compensating for an estimated channel value.Assuming that the reference signal transmitted by the transmitter is p,channel information experienced by the reference signal duringtransmission is h, thermal noise occurring in the receiver is n, and thesignal received by the receiver is y, it can result in y=h·p+n. Here,since the receiver already knows the reference signal p, it can estimatea channel information value ĥ using Equation 1 in the case in which aLeast Square (LS) method is used.

ĥ=y/p=h+n/p=h+{circumflex over (n)}  [Equation 1]

An uplink reference signal can be classified into a demodulationreference signal (DMRS) and a sounding reference signal (SRS). The DMRSis a reference signal used for channel estimation to demodulate areceived signal. The DMRS can be combined with PUSCH or PUCCHtransmission. The SRS is a reference signal transmitted for uplinkscheduling by a user equipment to a base station. The base stationestimates an uplink channel by using the received SRS, and the estimateduplink channel is used in uplink scheduling. The SRS can be transmittedperiodically, or can be transmitted aperiodically by being triggered bythe base station when the base station requires SRS transmission.

An aperiodic SRS transmission method has not been defined in a carrieraggregation system in which a plurality of component carriers (CCs) aredefined. In particular, there is a need to determine a specific CC usedfor aperiodic SRS transmission among the plurality of CCs.

SUMMARY OF THE INVENTION

The present invention provides an aperiodic transmission method andapparatus for a sounding reference signal in a wireless communicationsystem.

In an aspect, an aperiodic sounding reference signal (SRS) transmissionmethod performed by a user equipment (UE) in a wireless communicationsystem is provided. The method includes transmitting an aperiodic SRSthrough a specific uplink (UL) component carrier (CC) among a pluralityof UL CCs, wherein the specific UL CC is identical to the UL CC thattransmits a physical uplink shared channel (PUSCH) which is scheduled byan uplink grant, and wherein the uplink grant contains a message fortriggering the aperiodic SRS transmission.

The UL CC that transmits the PUSCH may be determined based on a downlinkcontrol information (DCI) format transmitted through the uplink grant.

The UL CC that transmits the PUSCH may be indicated by a carrierindicator field (CIF) in the DCI format.

The UL CC that transmits the PUSCH may be a UL CC linked to a downlink(DL) CC that transmits the uplink grant.

A link between the DL CC and the UL CC may be determined based on systeminformation.

The aperiodic SRS may be transmitted by being allocated to a resourceused for periodic SRS transmission in the specific UL CC.

The aperiodic SRS may be transmitted by being allocated to an availablewhole SRS bandwidth among respective system bandwidths in the specificUL CC.

The aperiodic SRS may be transmitted by being allocated to the greatestbandwidth among SRS bandwidths determined in a UE-specific manner in thespecific UL CC.

The aperiodic SRS may be transmitted by being allocated to some of theSRS bandwidths determined in a UE-specific manner in the specific UL CC.

The aperiodic SRS is transmitted through a plurality of antennas.

In another aspect, a UE in a wireless communication system is provided.The UE includes a radio frequency (RF) unit for transmitting anaperiodic SRS through a specific UL CC among a plurality of UL CCs, anda processor coupled to the RF unit, wherein the specific UL CC isidentical to the UL CC that transmits a PUSCH which is scheduled by anuplink grant, and wherein the uplink grant contains a message fortriggering the aperiodic SRS transmission.

According to the present invention, an uplink component carrier (CC)used for aperiodic sounding reference signal (SRS) transmission can beeffectively indicated in a carrier aggregation system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

FIG. 3 shows an example of a resource grid of a single downlink slot.

FIG. 4 shows the structure of a downlink subframe.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 shows an example of a transmitter and a receiver which constitutea carrier aggregation system.

FIG. 7 and FIG. 8 are other examples of a transmitter and a receiverwhich constitute a carrier aggregation system.

FIG. 9 shows an example of an asymmetric carrier aggregation system.

FIG. 10 shows the proposed aperiodic SRS transmission method accordingto an embodiment of the present invention.

FIG. 11 is a block diagram showing a BS and a UE to implement anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following technique may be used for various wireless communicationsystems such as code division multiple access (CDMA), a frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), singlecarrier-frequency division multiple access (SC-FDMA), and the like. TheCDMA may be implemented as a radio technology such as universalterrestrial radio access (UTRA) or CDMA2000. The TDMA may be implementedas a radio technology such as a global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by a radio technologysuch as IEEE (Institute of Electrical and Electronics Engineers) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (Evolved UTRA), andthe like. IEEE 802.16m, an evolution of IEEE 802.16e, provides backwardcompatibility with a system based on IEEE 802.16e. The UTRA is part of auniversal mobile telecommunications system (UMTS). 3GPP (3^(rd)generation partnership project) LTE (long term evolution) is part of anevolved UMTS (E-UMTS) using the E-UTRA, which employs the OFDMA indownlink and the SC-FDMA in uplink. LTE-A (advanced) is an evolution of3GPP LTE.

Hereinafter, for clarification, LET-A will be largely described, but thetechnical concept of the present invention is not meant to be limitedthereto.

FIG. 1 shows a wireless communication system.

The wireless communication system 10 includes at least one base station(BS) 11. Respective BSs 11 provide a communication service to particulargeographical areas 15 a, 15 b, and 15 c (which are generally calledcells). Each cell may be divided into a plurality of areas (which arecalled sectors). A user equipment (UE) 12 may be fixed or mobile and maybe referred to by other names such as MS (mobile station), MT (mobileterminal), UT (user terminal), SS (subscriber station), wireless device,PDA (personal digital assistant), wireless modem, handheld device. TheBS 11 generally refers to a fixed station that communicates with the UE12 and may be called by other names such as eNB (evolved-NodeB), BTS(base transceiver system), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. A BS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a MIMO(Multiple-Input Multiple-Output) system, a MISO (Multiple-InputSingle-Output) system, an SISO (Single-Input Single-Output) system, andan SIMO (Single-Input Multiple-Output) system. The MIMO system uses aplurality of transmission antennas and a plurality of receptionantennas. The MISO system uses a plurality of transmission antennas anda single reception antenna. The SISO system uses a single transmissionantenna and a single reception antenna. The SIMO system uses a singletransmission antenna and a plurality of reception antennas. Hereinafter,a transmission antenna refers to a physical or logical antenna used fortransmitting a signal or a stream, and a reception antenna refers to aphysical or logical antenna used for receiving a signal or a stream.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

It may be referred to Paragraph 5 of “Technical Specification GroupRadio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation (Release 8)” to 3GPP (3rdgeneration partnership project) TS 36.211 V8.2.0 (2008-03). Referring toFIG. 2, the radio frame includes 10 subframes, and one subframe includestwo slots. The slots in the radio frame are numbered by #0 to #19. Atime taken for transmitting one subframe is called a transmission timeinterval (TTI). The TTI may be a scheduling unit for a datatransmission. For example, a radio frame may have a length of 10 ms, asubframe may have a length of 1 ms, and a slot may have a length of 0.5ms.

One slot includes a plurality of OFDM (Orthogonal Frequency DivisionMultiplexing) symbols in a time domain and a plurality of subcarriers ina frequency domain. Since 3GPP LTE uses OFDMA in downlink, the OFDMsymbols are used to express a symbol period. The OFDM symbols may becalled by other names depending on a multiple-access scheme. Forexample, when SC-FDMA is in use as an uplink multi-access scheme, theOFDM symbols may be called SC-FDMA symbols. A resource block (RB), aresource allocation unit, includes a plurality of continuous subcarriersin a slot. The structure of the radio frame is merely an example.Namely, the number of subframes included in a radio frame, the number ofslots included in a subframe, or the number of OFDM symbols included ina slot may vary.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE can be simultaneously performed. In a TDDsystem in which an uplink transmission and a downlink transmission arediscriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows an example of a resource grid of a single downlink slot.

A downlink slot includes a plurality of OFDM symbols in the time domainand N_(RB) number of resource blocks (RBs) in the frequency domain. TheN_(RB) number of resource blocks included in the downlink slot isdependent upon a downlink transmission bandwidth set in a cell. Forexample, in an LTE system, N_(RB) may be any one of 60 to 110. Oneresource block includes a plurality of subcarriers in the frequencydomain. An uplink slot may have the same structure as that of thedownlink slot.

Each element on the resource grid is called a resource element. Theresource elements on the resource grid can be discriminated by a pair ofindexes (k,l) in the slot. Here, k (k=0, . . . , N_(RB)×12-1) is asubcarrier index in the frequency domain, and 1 is an OFDM symbol indexin the time domain.

Here, it is illustrated that one resource block includes 7×12 resourceelements made up of seven OFDM symbols in the time domain and twelvesubcarriers in the frequency domain, but the number of OFDM symbols andthe number of subcarriers in the resource block are not limited thereto.The number of OFDM symbols and the number of subcarriers may varydepending on the length of a cyclic prefix (CP), frequency spacing, andthe like. For example, in case of a normal CP, the number of OFDMsymbols is 7, and in case of an extended CP, the number of OFDM symbolsis 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively usedas the number of subcarriers in one OFDM symbol.

FIG. 4 shows the structure of a downlink subframe.

A downlink subframe includes two slots in the time domain, and each ofthe slots includes seven OFDM symbols in the normal CP. First three OFDMsymbols (maximum four OFDM symbols with respect to a 1.4 Mhz bandwidth)of a first slot in the subframe corresponds to a control region to whichcontrol channels are allocated, and the other remaining OFDM symbolscorrespond to a data region to which a physical downlink shared channel(PDSCH) is allocated.

The PDCCH may carry a transmission format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a PCH, systeminformation on a DL-SCH, a resource allocation of an higher layercontrol message such as a random access response transmitted via aPDSCH, a set of transmission power control commands with respect toindividual UEs in a certain UE group, an activation of a voice overinternet protocol (VoIP), and the like. A plurality of PDCCHs may betransmitted in the control region, and a UE can monitor a plurality ofPDCCHs. The PDCCHs are transmitted on one or an aggregation of aplurality of consecutive control channel elements (CCE). The CCE is alogical allocation unit used to provide a coding rate according to thestate of a wireless channel. The CCD corresponds to a plurality ofresource element groups. The format of the PDCCH and an available numberof bits of the PDCCH are determined according to an associative relationbetween the number of the CCEs and a coding rate provided by the CCEs.

The BS determines a PDCCH format according to a DCI to be transmitted tothe UE, and attaches a cyclic redundancy check (CRC) to the DCI. Aunique radio network temporary identifier (RNTI) is masked on the CRCaccording to the owner or the purpose of the PDCCH. In case of a PDCCHfor a particular UE, a unique identifier, e.g., a cell-RNTI (C-RNTI), ofthe UE, may be masked on the CRC. Or, in case of a PDCCH for a pagingmessage, a paging indication identifier, e.g., a paging-RNTI (P-RNTI),may be masked on the CRC. In case of a PDCCH for a system informationblock (SIB), a system information identifier, e.g., a systeminformation-RNTI (SI-RNTI), may be masked on the CRC. In order toindicate a random access response, i.e., a response to a transmission ofa random access preamble of the UE, a random access-RNTI (RA-RNTI) maybe masked on the CRC.

FIG. 5 shows the structure of an uplink subframe.

An uplink subframe may be divided into a control region and a dataregion in the frequency domain. A physical uplink control channel(PUCCH) for transmitting uplink control information is allocated to thecontrol region. A physical uplink shared channel (PUCCH) fortransmitting data is allocated to the data region. When indicated by ahigher layer, the UE may support a simultaneous transmission of thePUSCH and the PUCCH.

The PUCCH with respect to a UE is allocated by a pair of resource blocksin a subframe. The resource blocks belonging to the pair of resourceblocks (RBs) occupy different subcarriers in first and second slots,respectively. The frequency occupied by the RBs belonging to the pair ofRBs is changed based on a slot boundary. This is said that the pair ofRBs allocated to the PUCCH are frequency-hopped at the slot boundary.The UE can obtain a frequency diversity gain by transmitting uplinkcontrol information through different subcarriers according to time. InFIG. 5, m is a position index indicating the logical frequency domainpositions of the pair of RBs allocated to the PUCCH in the subframe.

Uplink control information transmitted on the PUCCH may include a hybridautomatic repeat request (HARQ) acknowledgement/non-acknowledgement(ACK/NACK), a channel quality indicator (CQI) indicating the state of adownlink channel, an scheduling request (SR), and the like.

The PUSCH is mapped to a uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

3GPP LTE-A supports a carrier aggregation system. 3GPP TR 36.815 V9.0.0(2010-3) may be incorporated herein by reference to describe the carrieraggregation system.

The carrier aggregation system implies a system that configures awideband by aggregating one or more carriers having a bandwidth smallerthan that of a target wideband when the wireless communication systemintends to support the wideband. The carrier aggregation system can alsobe referred to as other terms such as a bandwidth aggregation system orthe like. The carrier aggregation system can be divided into acontiguous carrier aggregation system in which carriers are contiguousto each other and a non-contiguous carrier aggregation system in whichcarriers are separated from each other. In the contiguous carrieraggregation system, a guard band may exist between CCs. A CC which is atarget when aggregating one or more CCs can directly use a bandwidththat is used in the legacy system in order to provide backwardcompatibility with the legacy system. For example, a 3GPP LTE system cansupport a bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20MHz, and a 3GPP LTE-A system can configure a wideband of 20 MHz orhigher by using only the bandwidth of the 3GPP LTE system.Alternatively, the wideband can be configured by defining a newbandwidth without having to directly use the bandwidth of the legacysystem.

In the carrier aggregation system, a UE can transmit or receive one or aplurality of carriers simultaneously according to capacity. An LTE-A UEcan transmit or receive a plurality of carriers simultaneously. An LTErel-8 UE can transmit or receive only one carrier when each of carriersconstituting the carrier aggregation system is compatible with an LTErel-8 system. Therefore, when the number of carriers used in uplink isequal to the number of carriers used in downlink, it is necessary toconfigure such that all CCs are compatible with LTE rel-8.

In order to efficiently use the plurality of carriers, the plurality ofcarriers can be managed in a media access control (MAC). Totransmit/receive the plurality of carriers, a transmitter and a receiverboth have to be able to transmit/receive the plurality of carriers.

FIG. 6 shows an example of a transmitter and a receiver which constitutea carrier aggregation system.

In the transmitter of FIG. 6( a), one MAC transmits and receives data bymanaging and operating all of n carriers. This is also applied to thereceiver of FIG. 6( b). From the perspective of the receiver, onetransport block and one HARQ entity may exist per CC. A UE can bescheduled simultaneously for a plurality of CCs. The carrier aggregationsystem of FIG. 6 can apply both to a contiguous carrier aggregationsystem and a non-contiguous carrier aggregation system. The respectivecarriers managed by one MAC do not have to be contiguous to each other,which results in flexibility in terms of resource management.

FIG. 7 and FIG. 8 are other examples of a transmitter and a receiverwhich constitute a carrier aggregation system.

In the transmitter of FIG. 7( a) and the receiver of FIG. 7( b), one MACmanages only one carrier. That is, the MAC and the carrier are 1:1mapped. In the transmitter of FIG. 8(a) and the receiver of FIG. 8( b),a MAC and a carrier are 1:1 mapped for some carriers, and regarding theremaining carriers, one MAC controls a plurality of CCs. That is,various combinations are possible based on a mapping relation betweenthe MAC and the carrier.

The carrier aggregation system of FIG. 6 to FIG. 8 includes n carriers.The respective carriers may be contiguous to each other or may beseparated from each other. The carrier aggregation system can apply bothto uplink and downlink transmissions. In a TDD system, each carrier isconfigured to be able to perform uplink transmission and downlinktransmission. In an FDD system, a plurality of CCs can be used bydividing them for an uplink usage and a downlink usage. In a typical TDDsystem, the number of CCs used in uplink transmission is equal to thatused in downlink transmission, and each carrier has the same bandwidth.The FDD system can configure an asymmetric carrier aggregation system byallowing the number of carriers and the bandwidth to be differentbetween uplink and downlink transmissions.

FIG. 9 shows an example of an asymmetric carrier aggregation system.

FIG. 9( a) shows an example of a carrier aggregation system in which thenumber of downlink CCs is greater than the number of uplink CCs.Downlink CCs #1 and #2 are linked to an uplink CC #1. Downlink CCs #3and #4 are linked to an uplink CC #2. FIG. 9( b) shows an example of acarrier aggregation system in which the number of downlink CCs isgreater than the number of uplink CCs. A downlink CC #1 is linked touplink CCs #1 and #2. A downlink CC #2 is linked to uplink CCs #3 and#4. Meanwhile, one transport block and one HARQ entity exist per CCwhich is scheduled from the perspective of a UE. Each transport block ismapped to only one CC. The UE can be mapped simultaneously to aplurality of CCs.

Hereinafter, an uplink reference signal (RS) will be described.

In general, an RS is transmitted as a sequence. Any sequence can be usedas a sequence used for an RS sequence without particular restrictions.The RS sequence may be a phase shift keying (PSK)-based computergenerated sequence. Examples of the PSK include binary phase shiftkeying (BPSK), quadrature phase shift keying (QPSK), etc. Alternatively,the RS sequence may be a constant amplitude zero auto-correlation(CAZAC) sequence. Examples of the CAZAC sequence include a Zadoff-Chu(ZC)-based sequence, a ZC sequence with cyclic extension, a ZC sequencewith truncation, etc. Alternatively, the RS sequence may be apseudo-random (PN) sequence. Example of the PN sequence include anm-sequence, a computer generated sequence, a Gold sequence, a Kasamisequence, etc. In addition, the RS sequence may be a cyclically shiftedsequence.

The uplink RS can be classified into a demodulation reference signal(DMRS) and a sounding reference signal (SRS). The DMRS is an RS used forchannel estimation to demodulate a received signal. The DMRS can becombined with PUSCH or PUCCH transmission. The SRS is an RS transmittedfor uplink scheduling by a UE to a BS. The BS estimates an uplinkchannel by using the received SRS, and the estimated uplink channel isused in uplink scheduling. The SRS is not combined with PUSCH or PUCCHtransmission. The same type of base sequences can be used for the DMRSand the SRS. Meanwhile, precoding applied to the DMRS in uplinkmulti-antenna transmission may be the same as precoding applied to thePUSCH. Cyclic shift separation is a primary scheme for multiplexing theDMRS. In an LTE-A system, the SRS may not be precoded, and may be anantenna-specific RS.

The SRS is an RS transmitted by a relay station to the BS and is an RSwhich is not related to uplink data or control signal transmission. Ingeneral, the SRS may be used for channel quality estimation forfrequency selective scheduling in uplink or may be used for otherusages. For example, the SRS may be used in power control, initial MCSselection, initial power control for data transmission, etc. In general,the SRS is transmitted in a last SC-FDMA symbol of one subframe.

An SRS sequence is defined as r_(SRS)(n)=r_(u,v) ^((α))(n). An RSsequence r_(u,v) ^((α))(n) can be defined based on a base sequenceb_(u,v)(n) and a cyclic shift α according to Equation 2.

r _(H,V) ^((α))(n)=e ^(jαn) b _(u,v)(n),0≦n<M _(sc) ^(RS)  [Equation 2]

In Equation 2, M_(sc) ^(RS) (1≦m≦N_(RB) ^(max,UL)) denotes an RSsequence length, where M_(sc) ^(RS)=m*N_(sc) ^(RB). N_(sc) ^(RB) denotesa size of a resource block represented by the number of subcarriers in afrequency domain. N_(RB) ^(max,UL) denotes a maximum value of an uplinkbandwidth expressed by a multiple of N_(sc) ^(RB). A plurality of RSsequences can be defined by differently applying a cyclic shift value ccfrom one base sequence.

The base sequence is divided into a plurality of groups. In this case,uε{0, 1, . . . , 29} denotes a group index, and v denotes a basesequence index in a group. The base sequence depends on a base sequencelength M_(sc) ^(RS). Each group includes one base sequence (i.e., v=0)having a length of M_(sc) ^(RS) with respect to m (where 1≦m≦5), andincludes two base sequences (i.e., v=0,1) having a length of M_(sc)^(RS) with respect to m (where 6≦m≦n_(RB) ^(max,UL)). The sequence groupindex u and the base sequence index v may vary over time similarly togroup hopping or sequence hopping to be described below.

In the SRS sequence, u denotes a PUCCH sequence group index, and vdenotes a base sequence index. A cyclic shift value cc is defined byEquation 3.

$\begin{matrix}{\alpha = {2\; \pi \frac{n_{SRS}^{cs}}{8}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

n_(SRS) ^(cs) denotes a value configured by a higher layer with respectto each UE, and may be any one integer in the range of 0 to 7.

The SRS sequence is mapped to a resource element by multiplying anamplitude scaling factor β_(SRS) to satisfy transmission power P_(SRS).The SRS sequence may be mapped to a resource element (k,l) starting fromr_(SRS)(0) according to Equation 4.

$\begin{matrix}{a_{{{2\; k} + k_{0}},l} = \left\{ \begin{matrix}{\beta_{SRS}{r^{SRS}(k)}} & {{k = 0},1,\ldots \mspace{14mu},{M_{{sc},b}^{RS} - 1}} \\0 & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, k₀ denotes a starting position in a frequency domain ofthe SRS, and M_(sc,b) ^(RS) denotes an SRS sequence length defined byEquation 5.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/2  [Equation 5]

In Equation 5, m_(SRS,b) can be given by Table 1 to Table 4 to bedescribed below with respect to each uplink bandwidth N_(RB) ^(UL).

k₀ of Equation 4 can be defined by Equation 6.

$\begin{matrix}{k_{0} = {k_{0}^{\prime} + {\sum\limits_{b = 0}^{B_{SRS}}\; {2\; M_{{sc},b}^{RS}n_{b}}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In Equation 6, k₀′ is defined as k′₀=(└N_(RB)^(UL)/2┘−m_(SRS,0)/2)N_(SC) ^(RB)+k_(TC) in a normal uplink subframe.k_(TC)ε{0,1} denotes a parameter given to a UE by a higher layer, andn_(b) denotes a frequency position index.

Frequency hopping of the SRS is configured by a parameterb_(hop)ε{0,1,2,3}given by the higher layer. If the frequency hopping ofthe SRS is not possible (i.e., b_(hop)≧B_(SRS)), it is determined as aconstant of the frequency position index n_(b)=└4 n_(RRC)/m_(SRS,b)┘ modN_(b), and n_(RRC) is given by the higher layer. If the frequencyhopping of the SRS is possible (i.e., b_(hop)<B_(SRS)), the frequencyposition index n_(b) can be determined by Equation 7.

$\begin{matrix}{n_{b} = \left\{ \begin{matrix}{\left\lfloor {4\; {n_{RRC}/m_{{SRS},b}}} \right\rfloor \mspace{14mu} {mod}\mspace{14mu} N_{b}} & {b \leq b_{hop}} \\{\left\{ {{F_{b}\left( n_{SRS} \right)} + \left\lfloor {4\; {n_{RRC}/m_{{SRS},b}}} \right\rfloor} \right\} \mspace{14mu} {mod}\mspace{14mu} N_{b}} & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

N_(b) can be determined by Table 1 to Table 4 to be described below, andF_(b)(n_(SRS)) can be determined by Equation 8.

$\begin{matrix}{{F_{b}\left( n_{SRS} \right)} = \left\{ \begin{matrix}\begin{matrix}{{\left( {N_{b}/2} \right)\left\lfloor \frac{n_{SRS}\mspace{14mu} {mod}\mspace{11mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}N_{b^{\prime}}}}{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}N_{b^{\prime}}} \right\rfloor} +} \\\left\lfloor \frac{n_{SRS}\mspace{11mu} {mod}\mspace{11mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}N_{b^{\prime}}}}{2\; {\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}N_{b^{\prime}}}} \right\rfloor\end{matrix} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {even}} \\{\left\lfloor {N_{b}/2} \right\rfloor \left\lfloor {n_{SRS}/{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {odd}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In Equation 8, n_(SRS) denotes the number of times of performingUE-specific SRS transmission, and can be determined by Equation 9.

$\begin{matrix}{n_{SRS} = \left\{ \begin{matrix}\begin{matrix}{{2\; N_{SP}n_{f}} +} \\{{2\left( {N_{SP} - 1} \right)\left\lfloor \frac{n_{s}}{10} \right\rfloor} +} \\{\left\lfloor \frac{T_{offset}}{T_{{offset}\_ \max}} \right\rfloor,}\end{matrix} & {{for}\mspace{14mu} 2\; {ms}\mspace{14mu} {SRS}\mspace{14mu} {periodicity}\mspace{14mu} {of}\mspace{14mu} {frame}\mspace{14mu} {structure}\mspace{14mu} 2} \\{\left\lfloor {\left( {{n_{f} \times 10} + \left\lfloor {n_{s}/2} \right\rfloor} \right)/T_{SRS}} \right\rfloor,} & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

In Equation 9, T_(SRS) denotes a UE-specific periodicity of SRStransmission, T_(offset) denotes an SRS subframe offset, and T_(offset)_(—) _(max) denotes a maximum value of the value T_(offset) for specificconfiguration of the SRS subframe offset. T_(SRS) and T_(offset) can begiven by Table 7 and Table 8 to be described below.

Table 1 to Table 4 show one example of SRS bandwidth configuration. A3-bit cell-specific parameter can be broadcast to indicate one bandwidthconfiguration among 8 bandwidth configurations. In addition, a 2-bitUE-specific parameter can be given from a higher layer to indicate onebandwidth configuration among 4 bandwidth configurations.

Table 1 shows an example of m_(SRS,b) and N_(b) (where, b=0,1,2,3) whenan uplink bandwidth N_(RB) ^(UL) is in the range of 6≦N_(RB) ^(UL)≦40.

TABLE 1 SRS bandwidth SRS- SRS- SRS- SRS- config- Bandwidth BandwidthBandwidth Bandwidth uration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS)= 3 C_(SRS) m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 36 112 3 4 3 4 1 1 32 1 16 2 8 2 4 2 2 24 1 4 6 4 1 4 1 3 20 1 4 5 4 1 4 1 416 1 4 4 4 1 4 1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 4 1 4 1 7 4 1 4 1 4 1 4 1

Table 2 shows an example of m_(SRS,b) and N_(b) (where, b=0, 1, 2, 3)when the uplink bandwidth N_(RB) ^(UL) is in the range of 40≦N_(RB)^(UL)≦60.

TABLE 2 SRS bandwidth SRS- SRS- SRS- SRS- config- Bandwidth BandwidthBandwidth Bandwidth uration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS)= 3 C_(SRS) m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 48 124 2 12 2 4 3 1 48 1 16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 41 4 32 1 16 2 8 2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 41 4 1

Table 3 shows an example of m_(SRS,b) and N_(b) (where, b=0, 1, 2, 3)when the uplink bandwidth N_(RB) ^(UL) is in the range of 60≦N_(RB)^(UL)≦80.

TABLE 3 SRS bandwidth SRS- SRS- SRS- SRS- config- Bandwidth BandwidthBandwidth Bandwidth uration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS)= 3 C_(SRS) m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 72 124 3 12 2 4 3 1 64 1 32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 1 24 2 12 24 3 4 48 1 16 3 8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 4 1 7 32 116 2 8 2 4 2

Table 4 shows an example of m_(SRS,b) and N_(b) (where, b=0, 1, 2, 3)when the uplink bandwidth N_(RB) ^(UL) is in the range of 80<N_(RB)^(UL)≦110.

TABLE 4 SRS bandwidth SRS- SRS- SRS- SRS- config- Bandwidth BandwidthBandwidth Bandwidth uration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS)= 3 C_(SRS) m_(SRS,0) N₀ m_(SRS,1) N₁ m_(SRS,2) N₂ m_(SRS,3) N₃ 0 96 148 2 24 2 4 6 1 96 1 32 3 16 2 4 4 2 80 1 40 2 20 2 4 5 3 72 1 24 3 12 24 3 4 64 1 32 2 16 2 4 4 5 60 1 20 3 4 5 4 1 6 48 1 24 2 12 2 4 3 7 48 116 3 8 2 4 2

In Table 1 to Table 4, a cell-specific parameter C_(SRS)ε{0, 1, 2, 3, 4,5, 6, 7} and a UE-specific parameter B_(SRS)ε{0, 1, 2, 3} are given by ahigher layer.

Table 5 and Table 6 show one example of a cell-specific subframeconfiguration period parameter T_(SFC) and a cell-specific subframeoffset parameter Δ_(SFC) for SRS transmission.

Table 5 shows one example of SRS subframe configuration in an FDDsystem. According to Table 5, the SRS subframe configuration can beindicted by a parameter having a length of 4 bits, and the periodicityof the SRS subframe may be any one of 1, 2, 5, and 10 subframes.

TABLE 5 Configuration Period Transmission T_(SFC) offset Δ_(SFC)srsSubframeConfiguration Binary (subframes) (subframes) 0 0000 1 {0} 10001 2 {0} 2 0010 2 {1} 3 0011 5 {0} 4 0100 5 {1} 5 0101 5 {2} 6 0110 5{3} 7 0111 5 {0, 1} 8 1000 5 {2, 3} 9 1001 10 {0} 10 1010 10 {1} 11 101110 {2} 12 1100 10 {3} 13 1101 10 {0, 1, 2, 3, 4, 6, 8} 14 1110 10 {0, 1,2, 3, 4, 5, 6, 8} 15 1111 reserved reserved

Table 6 shows one example of SRS subframe configuration in a TDD system.

TABLE 6 Configuration Period Transmission T_(SFC) offset Δ_(SFC)srsSubframeConfiguration Binary (subframes) (subframes) 0 0000 5 {1} 10001 5 {1, 2} 2 0010 5 {1, 3} 3 0011 5 {1, 4} 4 0100 5 {1, 2, 3} 5 01015 {1, 2, 4} 6 0110 5 {1, 3, 4} 7 0111 5 {1, 2, 3, 4} 8 1000 10 {1, 2, 6}9 1001 10 {1, 3, 6} 10 1010 10 {1, 6, 7} 11 1011 10 {1, 2, 6, 8} 12 110010 {1, 3, 6, 9} 13 1101 10 {1, 4, 6, 7} 14 1110 reserved reserved 151111 reserved reserved

The following operation is performed for SRS transmission by the UE.

When the UE transmits an SRS, transmission power P_(SRS) can bedetermined by Equation 10.

P _(SRS)(i)=min{P _(CMAX) ,P _(SRS) _(—) _(OFFSET)+10 log₁₀(M _(SRS))+P_(O) _(—) _(PUSCH)(j)+α(j)·PL+f(i)}  [Equation 10]

In Equation 10, i denotes a subframe index, P_(CMAX) denotes apredetermined UE's transmit power, P_(SRS) _(—) _(OFFSET) denotes a4-bit UE-specific parameter determined by the higher layer, M_(SRS)denotes an SRS transmission bandwidth expressed by the number ofresource blocks in a subframe having an index of i, and f(i) denotes acurrent power control regulation state for a PUSCH.

When the UE can select a transmit antenna, an index a(n_(SRS)) of a UEantenna for transmitting an SRS at a time n_(SRS) is defined asa(n_(SRS))=n_(SRS) mod 2 with respect to a whole sounding bandwidth or apartial sounding bandwidth when frequency hopping is not possible, andcan be defined by Equation 11 when frequency hopping is possible.

$\begin{matrix}{{a\left( n_{SRS} \right)} = \left\{ \begin{matrix}{\begin{pmatrix}{n_{SRS} + \left\lfloor {n_{SRS}/2} \right\rfloor +} \\{{\beta \cdot \left\lfloor {n_{SRS}/K} \right\rfloor}\;}\end{pmatrix}{mod}\mspace{14mu} 2} & {{when}\mspace{14mu} K\mspace{14mu} {is}\mspace{14mu} {even}} \\{n_{SRS}\mspace{14mu} {mod}\mspace{14mu} 2} & {{when}\mspace{14mu} K\mspace{14mu} {is}\mspace{14mu} {odd}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

In Equation 11, B_(SRS) denotes an SRS bandwidth, and b_(hop) denotes afrequency hopping bandwidth. N_(b) can be determined by a tablepredetermined by C_(SRS) and B_(SRS). Herein,

$\begin{matrix}{K = {\sum\limits_{b^{\prime} = b_{hop}}^{B_{SRS}}\; {N_{b^{\prime}}.}}} & \;\end{matrix}$

In Equation 11, β can be determined by Equation 12.

$\begin{matrix}{\beta = \left\{ \begin{matrix}1 & {{{where}\mspace{14mu} K\mspace{14mu} {mod}\mspace{14mu} 4} = 0} \\0 & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

When one SC-FDMA symbol exists in an uplink pilot time slot (UpPTS) in aTDD system, the SC-FDMA symbol can be used for SRS transmission. Whentwo SC-FDMA symbols exist in the UpPTS, both of the two SC-FDMA symbolscan be used for SRS transmission, and can be allocated simultaneously toone UE.

The UE does not transmit an SRS whenever SRS transmission and PUCCHformat 2/2a/2b transmission are simultaneously performed in the samesubframe.

If a parameter ‘ackNackSRS-SimultaneousTransmission’ is false, the UEdoes not transmit an SRS whenever SRS transmission and PUCCHtransmission for carrying ACK/NACK and/or positive SR are performed inthe same subframe. In addition, if the parameter‘ackNackSRS-SimultaneousTransmission’ is true, when SRS transmission andPUCCH transmission for carrying ACK/NACK and/or positive SR areconfigured in the same subframe, the UE transmits the PUCCH for carryingthe ACK/NACK and/or the positive SR simultaneously with the SRS by usinga shortened PUCCH format. That is, when the PUCCH for carrying theACK/NACK and/or the positive SR is configured in an SRS subframe whichis configured in a cell-specific manner, a shortened PUCCH format isused and the PUCCH for carrying the ACK/NACK and/or the positive SR istransmitted simultaneously with the SRS. When the SRS transmissionoverlaps a physical random access channel (PRACH) for a preamble format4 or exceeds a range of an uplink system bandwidth configured in a cell,the UE does not transmit the SRS.

The parameter ‘ackNackSRS-SimultaneousTransmission’ which is given bythe higher layer determines whether the UE supports simultaneoustransmission of an SRS and a PUCCH for carrying an ACK/NACK in onesubframe. If the UE is configured to simultaneously transmit the SRS andthe PUCCH for carrying the ACK/NACK in one subframe, the UE can transmitthe ACK/NACK and the SRS in a cell-specific SRS subframe. In this case,a shortened PUCCH format can be used, and transmission of the NACK or SRcorresponding to a position at which the SRS is transmitted ispunctured. The shortened PUCCH format is used in a cell-specific SRSsubframe even when the UE does not transmit the SRS in the subframe. Ifthe UE is configured not to simultaneously transmit the SRS and thePUCCH for carrying the ACK/NACK in one subframe, the UE can use a normalPUCCH format 1/1a/1b for transmission of the ACK/NACK and SR.

Table 7 and Table 8 show one example of UE-specific SRS configurationfor indicating an SRS transmission periodicity T_(SRS) and an SRSsubframe offset T_(offset). The SRS transmission periodicity T_(SRS) canbe determined from {2, 5, 10, 20, 40, 80, 160, 320} ms.

Table 7 shows one example of SRS configuration in an FDD system.

TABLE 7 SRS Configuration SRS Periodicity SRS Subframe Index I_(SRS)T_(SRS) (ms) Offset T_(offset) 0-1 2 I_(SRS) 2-6 5 I_(SRS)-2  7-16 10I_(SRS)-7 17-36 20 I_(SRS)-17 37-76 40 I_(SRS)-37  77-156 80 I_(SRS)-77157-316 160 I_(SRS)-157 317-636 320 I_(SRS)-317  637-1023 reservedreserved

Table 8 shows one example of SRS configuration in a TDD system.

TABLE 8 Configuration Index I_(SRS) SRS Periodicity T_(SRS) (ms) SRSSubframe Offset T_(offset) 0 2 0, 1 1 2 0, 2 2 2 1, 2 3 2 0, 3 4 2 1, 35 2 0, 4 6 2 1, 4 7 2 2, 3 8 2 2, 4 9 2 3, 4 10-14 5 I_(SRS) - 10 15-2410 I_(SRS) - 15 25-44 20 I_(SRS) - 25 45-84 40 I_(SRS) - 45  85-164 80I_(SRS) - 85 165-324 160 I_(SRS) - 165 325-644 320 I_(SRS) - 325 645-1023 reserved reserved

An SRS subframe satisfies (10*n_(f)+k_(SRS)−T_(offset)) mod T_(SRS)=0 inthe FDD system and, if T_(SRS)>2, in the TDD system. n_(f) denotes aframe index, and k_(SRS) denotes a subframe index in a frame in the FDDsystem. In the TDD system, if T_(SRS)=2, two SRS resources can beconfigured in a half-frame including at least one uplink subframe, andan SRS subframe satisfies (k_(SRS)−T_(offset)) mod 5=0.

In the TDD system, k_(SRS) can be determined by Table 9.

TABLE 9 subframe index n 1 6 1st 2nd 1st 2nd symbol symbol symbol symbolof of of of 0 UpPTS UpPTS 2 3 4 5 UpPTS UpPTS 7 8 9 k_(SRS) in case 0 12 3 4 5 6 7 8 9 UpPTS length of 2 symbols k_(SRS) in case 1 2 3 4 6 7 89 UpPTS length of 1 symbol

Meanwhile, the UE does not transmit an SRS whenever SRS transmission andPUSCH transmission corresponding to retransmission of the same transportblock are performed in the same subframe as a part of random accessresponse grant or contention-based random access procedure.

The SRS transmission method can be classified into two. As a methoddefined in LTE rel-8, there are a period SRS transmission method thatperiodically transmits an SRS according to an SRS parameter received byradio resource control (RRC) signaling and an aperiodic SRS transmissionmethod that transmits an SRS whenever necessarily on the basis of amessage dynamically triggered from a BS. The aperiodic SRS transmissionmethod can be used in LTE-A.

Meanwhile, in the periodic SRS transmission method and the aperiodic SRStransmission method, an SRS can be transmitted in a UE-specific SRSsubframe determined in a UE-specific manner. In a periodic SRStransmission method defined in LTE rel-8, a cell-specific SRS subframeis configured periodically by a cell-specific SRS parameter, andperiodic SRS transmission is performed in a periodic UE-specific SRSsubframe configured by a UE-specific SRS parameter among cell-specificSRS subframes. In this case, the periodic UE-specific SRS subframe maybe a subset of the cell-specific subframe. The cell-specific SRSparameter can be given by a higher layer. In the aperiodic SRStransmission method, an aperiodic SRS can be transmitted in an aperiodicUE-specific SRS subframe determined by a UE-specific aperiodic SRSparameter. The aperiodic UE-specific SRS subframe of the aperiodic SRStransmission method may be a subset of the cell-specific SRS subframe asdefined in the LTE rel-8. Alternatively, the aperiodic UE-specific SRSsubframe may be the same as the cell-specific subframe. The UE-specificaperiodic SRS parameter may also be given by a higher layer similarly tothe cell-specific SRS parameter. The UE-specific aperiodic SRS subframecan be configured by the aforementioned subframe periodicity andsubframe offset of Table 7 or Table 8.

In a carrier aggregation system including a plurality of CCs, anaperiodic SRS transmission method has not been defined. That is, when aBS requests aperiodic SRS transmission to a UE by using a specific DCIformat (i.e., when the BS triggers aperiodic SRS transmission), the UErequires information regarding a specific UL CC by which the UE performssounding and information regarding a specific resource used to performsounding.

Hereinafter, the present invention will be described according to anembodiment of the present invention.

FIG. 10 shows the proposed aperiodic SRS transmission method accordingto an embodiment of the present invention.

In step S100, a UE transmit an aperiodic SRS through a specific UL CCamong a plurality of UL CCs.

When a BS triggers the aperiodic SRS transmission by using one bit, theUE can transmit the aperiodic SRS through a UL CC determined by variousmethods.

1) The UE can transmit the aperiodic SRS through a predetermined UL CC.In this case, the predetermined UL CC may be any one of a primary CC(PCC) or a secondary CC (SCC), and may be a CC of which the PCC and theSCC are predetermined.

2) The UE can transmit the aperiodic SRS through a UL CC determined byRRC signaling or L1/L1 control signaling. When information on the UL CCthat transmits the aperiodic SRS is transmitted through the L1/L2signaling, this can be defined in a DL DCI format or a UL DCI format.When it is defined in the DL DCI format, the aperiodic SRS can betransmitted through a UL CC indicated by a carrier indicator field(CIF). Alternatively, the UL CC can be indicated by another field.

3) The UE can transmit the aperiodic SRS through some UL CCs amongconfigured UL CCs determined by RRC signaling. In this case, the some ULCCs that transmit the SRS may be indicated by RRC signaling or L1/L2control signaling.

4-1) The UE can transmit the aperiodic SRS through a UL CC linked to aDL CC that transmits a UL DCI format including a message for triggeringthe aperiodic SRS transmission. In this case, the link between the DL CCand the UL CC can be indicated by using an SIB-2 link relation.

4-2) The UE can transmit the aperiodic SRS through a UL CC linked to aDL CC that transmits a DL DCI format including a message for triggeringthe aperiodic SRS transmission. In this case, the link between the DL CCand the UL CC can be indicated by using an SIB-2 link relation.

4-3) The UE can transmit the aperiodic SRS through a UL CC to whichscheduling information is applied in a UL DCI format including a messagefor triggering the aperiodic SRS transmission. The UL CC to which thescheduling information is applied can be indicated by a CIF in the ULDCI format.

4-4) The UE can transmit the aperiodic SRS through a UL CC linked to aDL CC to which scheduling information is applied in a DL DCI formatincluding a message for triggering the aperiodic SRS transmission. TheUL CC to which the scheduling information is applied can be indicated bya CIF in the DL DCI format.

5) A UL CC that transmits the aperiodic SRS can be directly indicated byusing an additional control signal field allocated dynamically orsemi-dynamically.

6) The aperiodic SRS can be transmitted through a UL CC implicitlydetermined according to a UE state or configuration information of atransmission mode (i.e., a MIMO transmission mode or a non-contiguous RBallocation based transmission mode).

A resource for the aperiodic SRS transmission in a UL CC can beallocated in various manners.

1) As the resource for the aperiodic SRS transmission, a resource usedfor periodic SRS transmission can be directly used. That is, theresource can be allocated for the aperiodic SRS transmission on thebasis of SRS parameters such as cell-specific SRS bandwidthconfiguration information, UE-specific SRS bandwidth configurationinformation, transmission comb information, or the like which areprovided by RRC signaling or L1/L2 control signaling.

2) Irrespective of cell-specific SRS bandwidth configuration orUE-specific bandwidth configuration for the periodic SRS, an availablewhole band SRS bandwidth can be allocated for the aperiodic SRStransmission among respective system bandwidths defined in LTE rel-8/9.For example, for the aperiodic SRS transmission, 24 RBs, 48 RBs, 72 RBs,and 96 RBs are respectively allocated for system bandwidths 5 MHz, 10MHz, 15 MHz, and 20 MHz. In one subframe, a time resource for theaperiodic SRS transmission may be a last SC-FDMA symbol of a subframeused for periodic SRS transmission, and the aperiodic SRS and theperiodic SRS can be multiplexed in various manners.

3) Among SRS bandwidths that can be configured in a UE-specific mannerin the cell-specific SRS bandwidth configuration, the greatest bandwidthcan be allocated for the aperiodic SRS transmission. That is, this is acase where B_(SRS)=0 in Table 1 to Table 4.

4) The aperiodic SRS can be transmitted by using some bandwidths amongthe SRS bandwidths that can be configured in a UE-specific manner in thecell-specific SRS bandwidth configuration. For example, the SRSbandwidth that can be configured in a UE-specific manner can be dividedso as to transmit the aperiodic SRS in sequence by using each dividedbandwidth. Each divided bandwidth may have the same size. Alternatively,the aperiodic SRS can be transmitted by using a bandwidth greater than amaximum value of an SRS bandwidth that can be configured in aUE-specific manner. This implies that the UE can transmit the aperiodicSRS by using an SRS bandwidth which is different from the UE-specificSRS bandwidth allocated to the UE.

5) The aperiodic SRS can be transmitted by using a newly defined SRSresource, and the SRS resource can include a resource used for DMRStransmission.

6) The aperiodic SRS can be transmitted by using a time resource basedon a DCI format or a specific time resource for the aperiodic SRS in atime domain. For example, when the aperiodic SRS is triggered by the DLDCI, the aperiodic SRS can be transmitted in a UL subframe thattransmits a UL control signal corresponding to the DL DCI or can betransmitted in a UE-specific aperiodic SRS subframe which is a firstdefined SRS resource after the UL subframe. Alternatively, when theaperiodic SRS is triggered by the UL DCI, the aperiodic SRS can betransmitted in a UL subframe to which a corresponding UL resource isallocated or can be transmitted in a UE-specific aperiodic SRS subframewhich is a first defined SRS resource after the UL subframe.Alternatively, the aperiodic SRS can be transmitted according to aspecific offset predetermined or indicated by another signal, or can betransmitted in a UE-specific aperiodic SRS subframe which is an SRSresource first available at that time.

The aperiodic SRS can be multiplexed to be transmitted through aplurality of antennas.

1) A periodic SRS is transmitted through multiple antennas by arepetition factor (RPF) of 2. An aperiodic SRS can also be transmittedthrough the multiple antennas by the RPF of 2. For this, differenttransmission combs can be configured, and multiplexing can be performedby using code division multiplexing (CDM) by allocating different cyclicshift values in the same transmission comb.

2) The aperiodic SRS can be transmitted through the multiple antennas byusing another RPF value other than the RPF of 2.

3) Alternatively, the aperiodic SRS may not be transmittedsimultaneously for all antennas while the aperiodic SRS is transmittedthrough a plurality of antennas. That is, in the aperiodic SRStransmission, transmission can be performed such that each of theantennas are multiplexed according to time division multiplexing (TDM)through the plurality of antennas. A resource used in this case can betransmitted by using the same resource by each antenna. For example, aresource allocated for the periodic SRS transmission can be used for theaperiodic SRS transmission.

Meanwhile, an aperiodic SRS transmitted through a specific UL CC can betransmitted simultaneously with another SRS transmitted through anotherUL CC. When a resource for transmitting the aperiodic SRS does notoverlap with a resource for transmitting the periodic SRS, the UE cansimultaneously transmit the aperiodic SRS and the periodic SRS. In thiscase, the UE can transmit the aperiodic SRS and the periodic SRS througha plurality of UL CCs in various manners. For example, a UL CC thattransmits the aperiodic SRS may be a PCC, an anchor CC, or an SCC.Alternatively, the UL CC that transmits the aperiodic SRS may be some ULCCs among configured UL CCs determined by RRC signaling, and in thiscase, the some UL CCs that transmit the SRS can be indicated by RRCsignaling or L1/L2 control signaling.

Alternatively, the aperiodic SRS for the plurality of UL CCs can betransmitted through only one UL CC. The aperiodic SRS can be transmittedthrough one UL CC by being TDM-multiplexed on a subframe basis in theconfigured UL CC. Alternatively, the PCC and another UL CC can beTDM-multiplexed. Alternatively, the aperiodic SRS can be transmitted bybeing TDM-multiplexed on a subframe basis in a UL CC linked to a DL CCthat triggers aperiodic SRS transmission. Alternatively, the aperiodicSRS can be transmitted by being TDM-multiplexed on a subframe basis inall available UL CCs irrespective of a link between the DL CC and the ULCC. When transmitting the aperiodic SRS which is TDM-multiplexed, atransmission order of the aperiodic SRS can be indicated by a controlsignal or can be predetermined. When the aperiodic SRS transmissionoverlaps with periodic SRS transmission which is configured by RRC inadvance, the UE can drop the periodic SRS transmission, and can performonly the aperiodic SRS transmission. In this case, the dropping of theperiodic SRS transmission can be applied only when a UL CC thattransmits the aperiodic SRS and a UL CC that transmits the periodic SRSare the same UL CC. Alternatively, even if the UL CC that transmits theaperiodic SRS is different from the UL CC that transmits the periodicSRS, only the aperiodic SRS transmission can be performed while droppingthe periodic SRS transmission.

FIG. 11 is a block diagram of a BS and a UE according to an embodimentof the present invention.

A BS 800 includes a processor 810, a memory 820, and a radio frequency(RF) unit 830. The processor 810 implements the proposed functions,procedures, and/or methods. Layers of a radio interface protocol can beimplemented by the processor 810. The memory 820 coupled to theprocessor 810 stores a variety of information for driving the processor810. The RF unit 830 coupled to the processor 810 transmits and/orreceives a radio signal.

A UE 900 includes a processor 910, a memory 920, and an RF unit 930. Theprocessor 910 implements the proposed functions, procedures, and/ormethods. Layers of a radio interface protocol can be implemented by theprocessor 910. The memory 920 coupled to the processor 910 stores avariety of information for driving the processor 910. The RF unit 930coupled to the processor 910 transmits an aperiodic SRS through aspecific UL CC among a plurality of UL CCs. The specific UL CC is a ULCC which is the same as a UL CC that transmits a PUSCH scheduled by anuplink grant. The uplink grant includes a message for triggering theaperiodic SRS transmission.

The processor 910 may include an application-specific integrated circuit(ASIC), another chip set, a logical circuit, and/or a data processingunit. The RF unit 920 may include a baseband circuit for processingradio signals. In software implemented, the aforementioned methods canbe implemented with a module (i.e., process, function, etc.) forperforming the aforementioned functions. The module may be performed bythe processor 910.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for transmitting, by a user equipment(UE), an aperiodic sounding reference signal (SRS) in a wirelesscommunication system, the method comprising: receiving, via a physicaldownlink control channel (PDCCH), downlink control information (DCI)including an SRS request for triggering transmission of an aperiodicSRS; detecting the SRS request; if a carrier indicator field (CIF) isconfigured, transmitting the aperiodic SRS on a uplink (UL) componentcarrier (CC), among a plurality of UL CCs, corresponding to the CIF; andif a CIF is not configured, transmitting the aperiodic SRS on a UL CC,among the plurality of UL CCs, in which a physical uplink shared channel(PUSCH) is scheduled by the DCI.
 2. The method of claim 1, wherein theCIF is included in the DCI if the CIF is configured.
 3. The method ofclaim 1, wherein the DCI is received via the PDCCH on a downlink (DL) CClinked to the UL CC.
 4. The method of claim 3, wherein the linkagebetween the UL CC and the DL CC is indicated by system information. 5.The method of claim 1, wherein the aperiodic SRS is transmitted througha plurality of antennas.
 6. A user equipment (UE) in a wirelesscommunication system, the UE comprising: a radio frequency (RF) unit fortransmitting or receiving a radio signal; and a processor coupled to theRF unit, and configured to: receive, via a physical downlink controlchannel (PDCCH), downlink control information (DCI) including an SRSrequest for triggering transmission of an aperiodic SRS, detect the SRSrequest, if a carrier indicator field (CIF) is configured, transmit theaperiodic SRS on a uplink (UL) component carrier (CC), among a pluralityof UL CCs, corresponding to the CIF, and if a CIF is not configured,transmit the aperiodic SRS on a UL CC, among the plurality of UL CCs, inwhich a physical uplink shared channel (PUSCH) is scheduled by the DCI.7. The UE of claim 6, wherein the CIF is included in the DCI if the CIFis configured.
 8. The UE of claim 6, wherein the DCI is received via thePDCCH on a downlink (DL) CC linked to the UL CC.
 9. The UE of claim 8,wherein the linkage between the UL CC and the DL CC is indicated bysystem information.
 10. The UE of claim 6, wherein the aperiodic SRS istransmitted through a plurality of antennas.